[compiler] Functions, reborn

.chronus/changes/witemple-msft-extern-fn-2025-10-21-12-47-57.md

@@ -0,0 +1,7 @@
+---
+changeKind: feature
+packages:
+  - "@typespec/compiler"
+---
+
+Added support for Functions, a new type graph entity and language feature. Functions enable library authors to provide input-output style transforms that operate on types and values. See [the Functions Documentation](https://typespec.io/docs/language-basics/functions/) for more information about the use and implementation of functions.

.chronus/changes/witemple-msft-extern-fn-2025-10-21-12-48-30.md

@@ -0,0 +1,24 @@
+---
+changeKind: internal
+packages:
+  - "@typespec/events"
+  - "@typespec/html-program-viewer"
+  - "@typespec/http-client"
+  - "@typespec/http"
+  - "@typespec/json-schema"
+  - "@typespec/openapi"
+  - "@typespec/protobuf"
+  - "@typespec/rest"
+  - "@typespec/spector"
+  - "@typespec/sse"
+  - "@typespec/streams"
+  - "@typespec/tspd"
+  - "@typespec/versioning"
+  - "@typespec/xml"
+  - "@typespec/openapi3"
+  - "@typespec/http-server-csharp"
+---
+
+Updated `tspd` to generate extern function signatures. Regenerated all extern signatures.
+
+Corrected any exhaustive matches over type/value kinds to account for Function types/values.

cspell.yaml

@@ -144,6 +144,9 @@ words:
   - lropaging
   - lstrip
   - lzutf
+  - MACVMIMAGE
+  - MACVMIMAGEM
+  - marshal
   - mday
   - methodsubscriptionid
   - mgmt
@@ -280,6 +283,7 @@ words:
   - unioned
   - unionified
   - unionify
+  - unmarshal
   - unparented
   - unprefixed
   - unprojected
@@ -351,6 +355,10 @@ patterns:
   - name: Authorization_Basic
     description: Ignore Base64 authorization tokens
     pattern: "/Authorization: Basic\\s+\\S+/g"
+  - name: Todo
+    description: Ignore TODO comments with usernames
+    pattern: "/TODO[\\/\\s\\(][a-zA-Z0-9_-]+/g"
 ignoreRegExpList:
   - cursortest
   - Authorization_Basic
+  - Todo

packages/compiler/generated-defs/TypeSpec.Prototypes.ts-test.ts

@@ -7,4 +7,4 @@ import type { TypeSpecPrototypesDecorators } from "./TypeSpec.Prototypes.js";
 /**
  * An error here would mean that the exported decorator is not using the same signature. Make sure to have export const $decName: DecNameDecorator = (...) => ...
  */
-const _: TypeSpecPrototypesDecorators = $decorators["TypeSpec.Prototypes"];
+const _decs: TypeSpecPrototypesDecorators = $decorators["TypeSpec.Prototypes"];

packages/compiler/generated-defs/TypeSpec.ts-test.ts

@@ -7,4 +7,4 @@ import type { TypeSpecDecorators } from "./TypeSpec.js";
 /**
  * An error here would mean that the exported decorator is not using the same signature. Make sure to have export const $decName: DecNameDecorator = (...) => ...
  */
-const _: TypeSpecDecorators = $decorators["TypeSpec"];
+const _decs: TypeSpecDecorators = $decorators["TypeSpec"];

packages/compiler/src/core/binder.ts

@@ -13,6 +13,7 @@ import {
   EnumStatementNode,
   FileLibraryMetadata,
   FunctionDeclarationStatementNode,
+  FunctionImplementations,
   FunctionParameterNode,
   InterfaceStatementNode,
   IntersectionExpressionNode,
@@ -133,7 +134,6 @@ export function createBinder(program: Program): Binder {
 
     for (const [key, member] of Object.entries(sourceFile.esmExports)) {
       let name: string;
-      let kind: "decorator" | "function";
       if (key === "$flags") {
         const context = getLocationContext(program, sourceFile);
         if (context.type === "library" || context.type === "project") {
@@ -152,12 +152,24 @@ export function createBinder(program: Program): Binder {
             );
           }
         }
+      } else if (key === "$functions") {
+        const value: FunctionImplementations = member as any;
+        for (const [namespaceName, functions] of Object.entries(value)) {
+          for (const [functionName, fn] of Object.entries(functions)) {
+            bindFunctionImplementation(
+              namespaceName === "" ? [] : namespaceName.split("."),
+              "function",
+              functionName,
+              fn,
+              sourceFile,
+            );
+          }
+        }
       } else if (typeof member === "function") {
         // lots of 'any' casts here because control flow narrowing `member` to Function
         // isn't particularly useful it turns out.
         if (isFunctionName(key)) {
           name = getFunctionName(key);
-          kind = "decorator";
           if (name === "onValidate") {
             const context = getLocationContext(program, sourceFile);
             const metadata =
@@ -170,12 +182,9 @@ export function createBinder(program: Program): Binder {
             // nothing to do here this is loaded as emitter.
             continue;
           }
-        } else {
-          name = key;
-          kind = "function";
+          const nsParts = resolveJSMemberNamespaceParts(rootNs, member);
+          bindFunctionImplementation(nsParts, "decorator", name, member as any, sourceFile);
         }
-        const nsParts = resolveJSMemberNamespaceParts(rootNs, member);
-        bindFunctionImplementation(nsParts, kind, name, member as any, sourceFile);
       }
     }
   }